Acetabular reamer

ABSTRACT

An orthopaedic cutting tool which includes a partially hemispherical shell having a shell radius, and a base including a first circumferential base segment and a second circumferential base segment. The shell has a first part on one side of the first circumferential base segment and the second circumferential base segment, and a second part on another side of the first circumferential base segment and the second circumferential base segment. A first non-planar surface is connected to the first part, and the first non-planar surface has a first curvature not equal to the shell radius. A second non-planar surface is connected to the second part, and the second non-planar surface has a second curvature not equal to the shell radius.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to orthopaedic cutting tools, and, moreparticularly, to acetabular reamers.

2. Description of the Related Art

Minimally invasive surgical techniques have the advantage of reducingthe trauma to tissue surrounding the surgical site during a surgicalprocedure. The small incision that surgeons are using for minimallyinvasive hip surgery make it difficult to insert a current full sizehemispherical acetabular reamer through the small incision. However, thefull size hemispherical acetabular reamer cuts a full hemisphericalshape in the acetabulum with minimal wobbling and therefore provides anexcellent preparation for the hip joint prosthesis. Additionally, areamer is required to be connected to a driver, which is in turnconnected to a rotational tool. The driver has a specific structure atthe proximal (to the surgical site) end thereof, which is compatiblewith specific attachment mechanisms on the reamers. The driversrepresent an investment on the part of the medical institution where thesurgery is performed, and if the reamer is modified to be morecompatible with minimally invasive surgical techniques, the driverattachment mechanism may be correspondingly modified, which necessitatesthe purchase of both the driver and the reamer for the medicalinstitution. The purchase of a driver adds cost to the acquisition ofthe new reamer technology.

Orthopaedic reamers are known that cut off opposing segments of thehemispherical shell of the reamer. The resulting reamer, while having areduced profile in a certain orientation, is no longer rotationallysymmetric. The lack of rotational symmetry can cause vibration andwobbling of the reamer when in use. Such a cut-down reamer design cancut an irregular cavity in the acetabulum, for example, during hip jointreplacement surgery. An irregular cavity in the acetabulum can reducethe expected lifetime of the hip joint prosthesis, cause discomfort forthe patient and increase the wear in the artificial joint, among otherproblems. Additionally, a purpose of the hemispherical shell is that itprovides a debris retaining cavity for cut material, thereby minimizingthe surgical site contamination with the cut material from theacetabulum. By simply cutting off the sides of the reamer, such a reamerno longer provides a debris retaining cavity. Further, these reamerslose rigidity, which reduces the cutting performance of the reamer, andthe reliability. Yet further, these reamers are relatively difficult tomanufacture.

An acetabular reamer is known in which the shape of the reamer ismodified in that one or more sides of the reamer are removed, andreplaced with flat side surfaces which maintain the closed nature of theinterior cavity. However, such a reamer creates stress points at thejuncture of flat surfaces and the curved shell which can lead to cracksand failure of the reamer. Further, such a reamer is relativelydifficult to manufacture.

What is needed in the art is an acetabular reamer with a reduced profilewhich includes a debris retaining capability, which cuts well, and whichis relatively easy and cost effective to manufacture.

SUMMARY OF THE INVENTION

The present invention provides an orthopaedic cutting tool with apartially hemispherical shell which has a shell radius, a firstnon-planar surface and a second non-planar surface, where each of thenon-planar surfaces includes curvatures which are not equal to the shellradius.

The invention comprises, in one form thereof, an orthopaedic cuttingtool which includes a partially hemispherical shell having a shellradius, and a base including a first circumferential base segment and asecond circumferential base segment. The shell has a first part on oneside of the first circumferential base segment and the secondcircumferential base segment, and a second part on another side of thefirst circumferential base segment and the second circumferential basesegment. A first non-planar surface is connected to the first part, andthe first non-planar surface has a first curvature not equal to theshell radius. A second non-planar surface is connected to the secondpart, and the second non-planar surface has a second curvature not equalto the shell radius.

The invention comprises, in another form thereof, an orthopaedicassembly which includes a driver and an orthopaedic cutting toolconnected to the driver. The orthopaedic cutting tool includes apartially hemispherical shell having a shell radius, and a baseincluding a first circumferential base segment and a secondcircumferential base segment. The shell has a first part on one side ofthe first circumferential base segment and the second circumferentialbase segment, and a second part on another side of the firstcircumferential base segment and the second circumferential basesegment. A first non-planar surface is connected to the first part, andthe first non-planar surface has a first curvature not equal to theshell radius. A second non-planar surface is connected to the secondpart, and the second non-planar surface has a second curvature not equalto the shell radius.

The invention comprises, in yet another form thereof, a method ofreaming an acetabulum, including the steps of: providing an acetabularreamer including a partially hemispherical shell having a shell radius,and a base including a first circumferential base segment and a secondcircumferential base segment. The shell has a first part on one side ofthe first circumferential base segment and the second circumferentialbase segment, and a second part on another side of the firstcircumferential base segment and the second circumferential basesegment. A first non-planar surface is connected to the first part, andthe first non-planar surface has a first curvature not equal to theshell radius. A second non-planar surface is connected to the secondpart, and the second non-planar surface has a second curvature not equalto the shell radius; connecting the acetabular reamer to a driver; andreaming the acetabulum.

An advantage of the present invention is that it provides an orthopaediccutting tool for a minimally invasive surgical procedure.

Another advantage of the present invention is that it provides anorthopaedic cutting tool for a minimally invasive surgical procedurewhich maintains a debris retaining cavity.

Yet another advantage of the present invention is that it cuts well and,in particular, provides a good preparation of an acetabulum.

Yet another advantage of the present invention is that it is relativelyeasy and cost effective to manufacture.

Yet another advantage of the present invention is that it is compatiblewith existing driver attachment mechanisms.

Yet another advantage of the present invention is that it is compatiblewith existing drivers.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become more apparent and theinvention will be better understood by reference to the followingdescription of an embodiment of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is an exploded, fragmentary perspective view of an embodiment ofan orthopaedic assembly according to the present invention;

FIG. 2 is an assembled, fragmentary perspective view of the embodimentof FIG. 1;

FIG. 3 is a top view of the orthopaedic cutting tool of FIG. 1;

FIG. 4 is a cross-sectional view taken along section line 4-4 in FIG. 3;

FIG. 5 is a side view of the orthopaedic cutting tool of FIG. 1; and

FIG. 6 is an end view of the orthopaedic cutting tool of FIG. 1.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplification set out hereinillustrates one preferred embodiment of the invention, in one form, andsuch exemplification is not to be construed as limiting the scope of theinvention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly to FIGS. 1 and 2,there is shown an orthopaedic assembly 10 which generally includes adriver 12, and an orthopaedic cutting tool 14 connected to driver 12.

Driver 12 includes a shaft 16 which can be attached to a rotating tool(not shown), and a cutting tool attachment mechanism 18.

Orthopaedic cutting tool 14 (FIGS. 3-6) includes a partiallyhemispherical shell 20 having a shell radius 22, and a base 24 includinga first circumferential base segment 26 and a second circumferentialbase segment 28. Shell 20 has a first part 30 on one side of firstcircumferential base segment 26 and second circumferential base segment28, and a second part 32 on another side of first circumferential basesegment 26 and second circumferential base segment 28. A firstnon-planar surface 34 is connected to first part 30, where firstnon-planar surface 34 has a first curvature 36 not equal to shell radius22. A second non-planar surface 38 is connected to second part 32, wheresecond non-planar surface 38 has a second curvature 42 not equal toshell radius 22.

First curvature 36 can include a first radius 44 which is greater thanshell radius 22, for example. Second curvature 42 can include a secondradius 46 which is greater than shell radius 22, for example. Firstradius 44 is approximately equal to second radius 46. Alternatively,first curvature 36 and/or second curvature 42 can be parabolic shaped.Cutting tool 14 can include a first curved transition 48 between firstnon-planar surface 34 and partially hemispherical shell 20. Further,cutting tool 14 can include a second curved transition 50 between secondnon-planar surface 38 and partially hemispherical shell 20. Orthopaediccutting tool 14 can be an acetabular reamer, for shaping an acetabulumprior to the implantation of an acetabular cup during hip replacementsurgery, with a plurality of cutting teeth 52 in partially hemisphericalshell 20.

Different sizes of hips require different acetabular cup prosthesis, andacetabular reamers have different sizes to match a corresponding cupsize. In one particular acetabular reamer, shell radius 22 can beapproximately 1.0 inches, first and second radii 44, 46 can each be 1.3inches, first and second curved transitions 48, 50 can each be 0.105inch, and the shell 20 and first and second non-planar surfaces 34, 38can each have a thickness of 0.020 inch. These exemplary dimensionschange for different sizes of reamer 14. Also for different size reamer14, the proportional relationship between two or more radii may stay thesame, or may change.

Orthopaedic cutting tool 14 can further include a driver attachment 54connected to base 24, where driver attachment 54 is in the form of adiametral bar with a first end 58 and a second end 60 and a centeringdisk 62 therebetween, and where both first end 58 and second end 60 areconnected to base 24.

In use, the present inventon discloses a method of reaming anacetabulum, including the steps of: providing an acetabular reamer 14 aspreviously described; connecting acetabular reamer 14 to driver 12; andreaming the acetabulum. The providing step can include the step offorming a first curved transition 48 between first non-planar surface 34and partially hemispherical shell 20.

While this invention has been described as having a preferred design,the present invention can be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

1. An orthopaedic cutting tool, comprising: a partially hemisphericalshell having a shell radius, and a base including a firstcircumferential base segment and a second circumferential base segment,said shell including a first part on one side of said firstcircumferential base segment and said second circumferential basesegment, and a second part on another side of said first circumferentialbase segment and said second circumferential base segment; a firstnon-planar surface connected to said first part, said first non-planarsurface having a first curvature not equal to said shell radius; and asecond non-planar surface connected to said second part, said secondnon-planar surface having a second curvature not equal to said shellradius.
 2. The orthopaedic cutting tool of claim 1, wherein said firstcurvature includes a first radius which is greater than said shellradius.
 3. The orthopaedic cutting tool of claim 2, wherein said secondcurvature includes a second radius which is greater than said shellradius.
 4. The orthopaedic cutting tool of claim 3, wherein said firstradius is approximately equal to said second radius.
 5. The orthopaediccutting tool of claim 1, wherein at least one of said first curvatureand said second curvature is parabolic shaped.
 6. The orthopaediccutting tool of claim 1, further including a first curved transitionbetween said first non-planar surface and said partially hemisphericalshell.
 7. The orthopaedic cutting tool of claim 6, further including asecond curved transition between said second non-planar surface and saidpartially hemispherical shell.
 8. The orthopaedic cutting tool of claim1, wherein said orthopaedic cutting tool is an acetabular reamer with aplurality of cutting teeth in said partially hemispherical shell.
 9. Theorthopaedic cutting tool of claim 1, further including a driverattachment connected to said base, said driver attachment having a firstend and a second end with a centering disk therebetween, both said firstend and said second end being connected to said base.
 10. An orthopaedicassembly, comprising: a driver; and an orthopaedic cutting toolconnected to said driver, said orthopaedic cutting tool including: apartially hemispherical shell having a shell radius, and a baseincluding a first circumferential base segment and a secondcircumferential base segment, said shell including a first part on oneside of said first circumferential base segment and said secondcircumferential base segment, and a second part on another side of saidfirst circumferential base segment and said second circumferential basesegment; a first non-planar surface connected to said first part, saidfirst non-planar surface having a first curvature not equal to saidshell radius; and a second non-planar surface connected to said secondpart, said second non-planar surface having a second curvature not equalto said shell radius.
 11. The orthopaedic assembly of claim 10, whereinsaid first curvature includes a first radius which is greater than saidshell radius.
 12. The orthopaedic assembly of claim 11, wherein saidsecond curvature includes a second radius which is greater than saidshell radius.
 13. The orthopaedic assembly of claim 12, wherein saidfirst radius is approximately equal to said second radius.
 14. Theorthopaedic assembly of claim 10, wherein at least one of said firstcurvature and said second curvature is parabolic shaped.
 15. Theorthopaedic assembly of claim 10, further including a first curvedtransition between said first non-planar surface and said partiallyhemispherical shell.
 16. The orthopaedic assembly of claim 15, furtherincluding a second curved transition between said second non-planarsurface and said partially hemispherical shell.
 17. The orthopaedicassembly of claim 10, wherein said orthopaedic cutting tool is anacetabular reamer with a plurality of cutting teeth in said partiallyhemispherical shell.
 18. The orthopaedic assembly of claim 10, furtherincluding a driver attachment connected to said base, said driverattachment having a first end and a second end with a centering disktherebetween, both said first end and said second end being connected tosaid base.
 19. A method of reaming an acetabulum, comprising the stepsof: providing an acetabular reamer including a partially hemisphericalshell having a shell radius, and a base including a firstcircumferential base segment and a second circumferential base segment,said shell including a first part on one side of said firstcircumferential base segment and said second circumferential basesegment, and a second part on another side of said first circumferentialbase segment and said second circumferential base segment, saidacetabular reamer further including a first non-planar surface connectedto said first part, said first non-planar surface having a firstcurvature not equal to said shell radius, and a second non-planarsurface connected to said second part, said second non-planar surfacehaving a second curvature not equal to said shell radius; connectingsaid acetabular reamer to a driver; and reaming the acetabulum.
 20. Themethod of claim 19, wherein said providing step includes the step offorming a first curved transition between said first non-planar surfaceand said partially hemispherical shell.